<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    *{
      margin: 0;
      padding: 0;
      list-style: none;
    }
    .box{
      width: 300px;
      margin: 20px auto;
    }
    .ul_title{
      width: 380px;
      height: 30px;
      background-image: url('imgs/bg.jpg');
      text-align: center;
      line-height: 30px;
      box-sizing: border-box;
      cursor: pointer;
    }
    .title{
      float: left;
      margin-left: 13px;
    }
    li{
      width: 110px;
      background-image: url('imgs/libg.jpg');
    }
    .title ul{
      display: none;
    }
  </style>
</head>
<body>
  <div class="box">
    <ul class="ul_title">
      <li class="title">一级菜单1
        <ul class="menu">
          <li>一级菜单11</li>
          <li>一级菜单11</li>
          <li>一级菜单11</li>
        </ul>
      </li>
      <li class="title">二级菜单2
        <ul>
          <li>二级菜单22</li>
          <li>二级菜单22</li>
          <li>二级菜单22</li>
        </ul>
      </li>
      <li class="title">三级菜单3
        <ul>
          <li>三级菜单33</li>
          <li>三级菜单33</li>
          <li>三级菜单33</li>
        </ul>
      </li>
    </ul>
  </div>
  <script src="../../jquery-1.12.4.min.js"></script>
  <script>
    $('.title').mouseenter(function(){
      $(this).children('ul').stop().slideDown(1000);
    });
    $('.title').mouseleave(function(){
      $(this).children('ul').stop().slideUp(1000);
    });
  </script>
</body>
</html>